I would think the easiest thing to do is to take a taxi, but it will be kind of expensive. It is a good distance away. There are also flights between the two airport if you want to look into them.
You can also take the Air train to Jamaica. Transfer to the LIRR (long island rail road) to Penn Station. Transfer to a Trenton train on the New Jersey Transit that stops at the air port.
Enjoy
I would think the easiest